【作者】 石定贤；

【导师】 赵阳升；

【作者基本信息】 太原理工大学 ， 岩土工程， 2014， 博士

【摘要】 天然气水合物作为一种广泛蕴藏于深海沉积层与陆地冻土带的水合物藏,以其巨大的资源储量引起了科学界的广泛关注,对水合物相关技术的研究应用正方兴未艾,这其中,天然气水合物的合成、分解与原位开采的理论与技术多年来一直是水合物相关研究领域的焦点所在,其本质原因,一方面是因为其温和的制备条件和相对较高的储气能力越来越受到人们的重视,希望通过研究拓展应用空间；另一方面,也是由于当前社会发展日新月异,对能源的需求日渐增大,而不可再生资源的逐步减少使人们滋生了对未来新型能源的强烈渴求,等等。然而,受制备工艺、生长速度和最终储气量等方面的制约,水合物合成技术一直未得长足发展；在资源开采利用方面,也因为成藏条件复杂、储层物性参数不明、开采过程不确定因素较多、水合物分解和运移机理复杂等方面的原因一直停滞不前。本文以气体水合物的强化制备工艺、分解开采理论为课题,在综合分析前人研究成果的基础上,独创性的设计并建立了首个适合于工业生产条件下的小型天然气水合物喷雾强化合成实验平台,并利用该平台对气体水合物强化合成工艺进行了探索性研究,深入分析了其强化的技术和机理,在此基础上,展开了多孔介质中气体水合物的合成及分解过程的CT扫描实验研究工作,并对具备下覆游离气层的天然气水合物藏降压开采以及海底水合物藏的原位注热水驱替开采理论和技术进行了详细研究,主要研究内容及成果如下：(1)进行了天然气水合物强化合成工艺研究。研制了适合工业生产的雾化型合成设备,可通过一次装样配合增压泵实现恒压不等容试验,或者封闭装样的恒容不等压试验,还可以通过补充或排出气体或水,实现恒压等容试验方式等。应用本套设备可研究工业化生产条件下各宏观可控因素如气体组成、气水混合方式、温度压力条件、水的成分等对水合物生成过程的具体影响及其作用机理,分析、研究气体水合物生成过程中热力学、动力学原理。(2)探寻了雾化平台下气体水合物合成的强化机理及关键因素。研究表明,雾化系统中诱导现象不明显,生长速度极快、含气量极高；整个生长过程受传质条件主导,传热条件不理想会严重影响生长速度,但传质条件不理想将首先导致反应过程缓慢、最终含气量大幅降低；在保证良好的传热条件下,生长速度对压力依赖明显,并且表现出明显的递增关系,压力越高,速度越快,过冷过压能有效加快生长进程；此外,活性剂、晶种、重复生成等都能显著加快反应进程,提高最终含气量。(3)展开了多孔介质水合物合成实验研究。多孔介质中气体水合物形成条件类似水溶液中,其气耗随时间变化可以分为三个阶段,称为起始合成段、快速合成段、合成完成段。起始合成段压力和温度波动较小,气耗也较小；快速合成段气体消耗速率快,温度和压力变化极为频繁,均系气体大幅度由气态向结晶态转化造成；合成完成段气耗率极低,以极低的速率延续至反应停止。多孔介质中生成水合物并不是仅限在试件表面,而是在试件内部的孔隙中全部生成和赋存,而且是均匀分布的,这是多孔介质天然气水合物的一个重要特征。(4)进行了多孔介质中水合物分解的CT扫描实验研究。多孔介质水合物分解时,随粒径的增大,其水合物分解的垂向移动量逐渐增大,对应的变形平均0.953%,这就是散体砂粒组成的多孔介质水合物分解的垂向变形量。垂向变形与砂粒直径呈指数变化规律,Uz=0.0032exp (0.4318d)。(5)研究了降压开采理论及技术。基于多相渗流理论与水合物分解动力学,建立了适合于开采具备下覆游离气层的水合物藏的降压开采过程的数学模型,并针对问题的强非线性,首次引入全隐式方法对控制方程进行了离散,给出了详细的差分解法,该法隐式程度高,求解过程更稳定,适用范围较常见的IMPES方法更为广泛,并应用FORTRAN语言编制了相应的计算程序,验证了数学模型及离散方法的准确性,运用该程序能准确获得开采过程中各场变量在各时刻的空间分布情况,获得其开采前缘移动位置及气、水的产出与运移规律。(6)探寻了降压开采过程中水合物分解和气水运移的本质规律。通过对降压开采的数值模拟结果表明,降压开采过程储层压力下降较为平缓,开采过程稳定性较好,通过降低井底流压可有效提高水合物藏开采速率,通过调整井底流压也能够兼顾开采速度与储层稳定性之间的平衡。从气水的产出运移过程来看,开采效率高低与储层绝对渗流率有较大关系,其值越大,运移越快,生产效率越高；相同绝对渗透率条件下,运移过程受渗透率下降指数的取值影响相对较小。(7)研究了注热驱替开采过程的固、流、热、分解的多场耦合理论。针对深海中水合物藏开采问题,建立了能够准确描述多孔介质中气体水合物注热开采过程的多场耦合数学模型。采用有限元和有限差分法结合对方程进行了离散,给出了其数值解法。通过编制计算程序,对海底水合物藏原位注热水驱替开采过程进行了数值模拟,验证了数学模型的准确性。通过模拟,能够准确的获得流体压力、介质温度、固体位移及变形等场变量的空间分布。(8)研究了注热驱替开采过程中耦合作用规律。从数值模拟的结果来看,典型的注采过程一般可分为前期的降压引导、中期的注热驱替及后期的缓慢分解三个阶段。中间的注热驱替过程水合物分解极快,气水产量很大,前期、后期的分解过程相对缓慢。注采过程存在一个极其明显的、呈带状分布的分解前沿,该带型区域内相态变化剧烈,水合物分解极快,是主导整个注采过程的关键阶段,大部分的水合物分解在该分解带的推进过程中完成。注热开采过程中压力提升较快、水的驱替作用明显。通过提高注入温度,可有效提高开采速度和最终产气量。综合分析表明,单纯的注热开采将在储层中产生较大的热量损耗,这是影响注采过程经济性的一个重要因素,可通过优化井网布置,合理配置注入剂量,施行降压注热结合的方式予以解决。更多还原

【Abstract】 As an extensive reserves of gas hydrates in deep-sea sediments hydrate reservoir and land tundra, gas hydrate has caused widespread concern in the scientific community with its huge reserves. The study of Hydrate technology research applications is ascendant, in which the synthesis, decomposition of gas hydrates, In-situ mining theory and technique has been the focus of research in the field of hydrate. The essential reason is partly because its mild conditions and relatively high gas storage capacity is getting more and more people’s attention who hope to achieve a wider range of applications through research, in the other hand, is due to the increasing demand for energy of current social processes, and gradually reducing non-renewable resources which make people had a strong desire for future breeding of new energy, and so on. However, restricting of the preparation process, the growth rate and final amount made gas hydrate synthesis techniques have been not developed smoothly. In addition, because of complex metallogenic conditions, uncertain factors in mining process, complex hydrate decomposition and migration mechanism, and the physical parameters of reservoir which have been unable to accurately explore, the resources utilization has stagnanted.’The improved preparation technology of gas hydrate, decomposition mining theory" is the topic of study, on the basis of comprehensive analysis of the predecessors research achievements, the research ingeniously designs and sets up the first small gas hydrates spray reinforced synthetic experiment platform suitable for industrial production condition. By using this platform, exploratory research has been carried on the improved synthesis process of gas hydrate, and deep analysis study has been conducted on the technology and mechanism of reinforcement. On this basis, the synthesis and decomposition of gas hydrate in porous media of computed tomography (CT) scanning experiment research has been further carried out, the detailed study has carried on the covering of free gas hydrate step-down mining, submarine gas hydrates, hidden note in-situ in the hot water for mining theory and technology. The main research contents and results are as follows:(l)We carry on the improved synthetic process gas hydrate study. The atomization synthesis equipment Suitable for industrial production was developed, through a sample loading range with booster pump it can achieve constant pressure test, or closed sample loading constant volume range compression test, and through complement or exhaust gas or water, it also can realize the constant pressure capacity test way. With this set of equipment we can study industrial production under the condition of macroscopic controllable factors, such as gas composition, gas water mixed method, temperature and pressure condition, the composition of water, the specific impact of hydrate formation process and its mechanism of action. We also can explore the thermodynamics and kinetics principle in the process of gas hydrate formation.(2) The research Explore the strengthening mechanism of atomization gas hydrate synthesis of lans and key factors. Studies show that atomization system induction phenomenon is not obvious, the growth speed is extremely fast, air content is too high; The whole growth process is dominanted by mass transfer conditions, the non-ideal heat transfer conditions will seriously affect the growth rate, but non-ideal mass transfer condition will be the first to slow reaction process, then finally bring about air content great reduction;In the condition of ensuring good heat transfer, the growth speed depend on pressure obviously, also showed distinct increment relation:the higher the pressure, the faster the speed, super-cooling and overpressure can effectively accelerate the growth process, In addition, surfactant, seed and repeat generation can significantly speed up the reaction process, improve the air content in the end(3)Study has been conducted on porous media hydrate synthesis experiment, gas hydrate formation conditions in porous media is similar in aqueous solution, the gas consumption changing with time can be divided into three section called the initial synthesis section, rapid synthesis section and complete section. Initial synthetic segments of the pressure and temperature fluctuations are small, gas consumption is small too. In the rapid synthesis segment gas consumption rate, temperature and pressure change very frequently, which are caused by gas transformation from gas to amorphous significantly, in the synthesis completion segment gas consumption rate is extremely low, and continue at a very low rate until reaction stoping. To generate hydrate in porous media is not only on the surface of the specimen, but all in the specimen within the pore formation and occurrence, and it is evenly distributed, this is an important feature of gas hydrate in porous media.(4)The hydrate decomposition of CT scan was carried on in the experimental study of porous medium. When porous medium hydrates decompose, along with the increase of particle size its hydrate decomposition vertical movement is gradually increasing, the corresponding deformation on average0.953%, this is the medium of sand porous media hydrate decomposition of vertical deformation. The vertical deformation and sand grain diameter exponential change rule exponentially, Uz=0.0032exp(0.4318d).(5)We studied the step-down mining theory and technology. Based on the theory of multiphase seepage and hydrate decomposition dynamics, we set up mathematical model of step-down the mining process which are suitable for the dissociation of gas hydrate with the mining, in view of the strongly nonlinear problems, fully implicit method is firstly introduced to the discrete control equations, the detailed difference method is gived. For the method, the implicit degree is high, the solving process is more stable, its broader scope of application is more common than IMPES method, and a corresponding calculating program was compiled with FORTRAN language, with which the accuracy of the mathematical model and discrete method was verified. The program can accurately obtain mining in the process of spatial distribution of the field variables in each time, it also can obtained the mining moving front position and the output and migration regularity of gas, water.(6)The research explores the essence of the law of the hydrate decomposition and gas-water move in the process of step-down mining. By the numerical simulation of depressurization mining results show that in the step-down production process the reservoir pressure drop is relatively flat and the stability is better, by reducing the bottom hole flowing pressure it can effectively improve the hydrate production rate, besides by adjusting the bottom hole flowing pressure it is also able to juggle mining balance between speed and stability of the reservoir. From the point of gas-water output of the migration process, whether mining efficiency is high have a great relationship with reservoir absolute seepage rate:the greater its value, the faster the migration, the production efficiency is higher; under the condition of absolute same permeability, migration process affected by the values of permeability decline index is relatively small.(7)We studied the solid, flow, heat, decomposition of many field coupling theory in the process of thermal displacement mining. Aimed at hydrate mining problem in deep sea, many field coupling mathematical model of thermal production process is established which can accurately describe the gas hydrate in porous media. The equation is discreted by finite element finite and difference method, then its numerical solution is given. By computing program, the submarine water hydrates situ thermial mining process are simulated, which verified the accuracy of the mathematical model. Through simulation, it can accurately obtain field variables spatial distribution such as fluid pressure, medium temperature, solid displacement and deformation.(8)We studied the thermal displacement coupling effect laws in the process of mining. From the point of the results of numerical simulation, the typical injection-production process generally can be divided into three stages:early decompression guide, medium-term thermal displacement and the later slow decomposition. In the middle of the thermal displacement process hydrate decompose fast, gas water production is very big, early, later decomposition process is relatively slow. During the injection-production process an extremely obvious, zonal distribution decomposition front existed, there phase change drastically, hydrate decompose extremely fast, which is the key to dorminant the injection-production process stage, most of the hydrate decomposition accomplish in the complete process of the decomposition zone. In the injection hot mining progress pressure increase rapidly, water displacement effect is obvious. By improving the injection temperature, it can effectively improve the mining speed and final gas production. Comprehensive analysis shows that the pure thermal production will produce larger heat loss in the reservoir, it is an key factor affect the injection-production process economy efficiency, which can be solve through optimization of well pattern arrangement, and rational allocation of injection dosage, way combiningstep-down with thermal.更多还原